I bought a used bike on craigslist, for cheap, and while I wasn't expecting it to be great the brakes and changing gears don't work perfectly.

The front brakes are very tight and the back ones are pretty loose... I can stop and everything but just would rather have a better performing system.

The gears change but sometimes don't work that well and I have to move the shifters all around for it to "stick" in a gear. Is there some way to simplify the gear structure? I wouldn't mind a single or fixed gear transition (since I live in NYC) but still want the ability to coast and use my brakes (assuming I can fix those too)

Welcome to Bicycles! This really seems like two questions (brakes and gears) and it would be better to ask them as two separate questions. Also, some details about the parts in question (for the brake question: brakes, brake levers and cables. For the gear question probably the most important would be details about the rear wheel and dropout). Pictures of the components would be good. I believe you don't have enough rep to post pictures inline yet, but if you include a link somebody else can fix it to be an inline picture.
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freiheit♦Nov 22 '11 at 18:47

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I think maybe your best next step would be to buy a book on basic bike maintenance. There should be some recommendations around somewhere.
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Daniel R HicksNov 22 '11 at 19:27

5 Answers
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It may be that your brakes and gears are simply out of adjustment. The easiest way to confirm this would be to take it to your local bike store (LBS) and ask them for advice. Most stores are pretty friendly and helpful towards keen amateurs.

If they advise that it's just adjustments they can do it themselves, or show you the adjustment screws so you can try it yourself.

More significant work

It may turn out that there is more work required, such as replacing brakes or gears. Also the chain, cassette and chainrings may need replacing.

In this case I'd be very wary of investing too much money into the bike. Buying components individually is a lot more expensive than buying a complete bike. Plus making sure parts will fit can be confusing and unreliable. If there's much wrong with the bike I'd say it'd be cheaper to buy a new bike where you know that all the parts are at least compatible and in good condition.

The friendly volunteers in your local co-op can teach you how to fix your bike. Co-ops also have a wide variety of tools you can use. Shop time is often as cheap as USD$5 to USD$10 per hour. They may also have a library of books you can read. As well, they may rent out tools for you to bring home.

Ensure that the brakes pads are not worn out and sitting a decent distance from the rim. If you can't see a minimum wear line, it's time to replace your pads. If the brakes are sitting more than a couple of millimeters from the rim, you will have to adjust the system. If there's a barrel adjuster somewhere in the brake line, turn it counter-clockwise a few times until the brake is sitting closer to the rim. Be careful here that you don't introduce a brake-rub, as an untrue wheel may wobble into the pads. If there is more slack than can be taken up with the barrel adjuster, screw it all the way in again and redo the tension by undoing the bolt fastening the cable to the brake. Also, if it's a road style caliper make sure that the quick release lever is flipped down.

Clean the braking surface and the surface of the pad. Grey gunk builds up on your braking surface over time. It can be cleaned off with elbow grease and steel wool. If the surface of the pads look at all glazed, rough them up with a course grit sandpaper.

Ensure that your cables are moving freely. If you notice that you are pulling the brake lever and the cable isn't moving much at the brake, you likely have rust in your housing. Often letting some oil work it's way into the end of the housing, then letting it sit will clear this up. (synthetic chain lube preferably, but wd40 would probably work too). If that doesn't do it, the housings and cables should be replaced.

We're looking for long answers that provide some explanation and context. Don't just give a one-line answer; explain why your answer is right, ideally with citations. Answers that don't include explanations may be removed.

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Welcome to Bicycles! Whilst this may theoretically answer the question, it would be preferable to include the essential parts of the answer here, and provide the link for reference. Perhaps put in the basics about adjusting brakes and switching a bike to singlespeed (or tuning the shifting)?
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freiheit♦Nov 23 '11 at 23:10

I would suggest learning to adjust the setup on your bike before anything else.

If you're mechanically minded, get your hands dirty and have a play around. If you're not, a bicycle is a great place to start your learning, and you can always take it to a bike store if it frustrates you too much. There are a lot of youtube videos on the subject if you prefer them over books:

Adjusting brakes:

Adjusting your rear derailleur, which is often the cause of gear troubles:

You'll first want to check the back wheel is true and aligned correctly. Sometimes going over gutters and bumps can knock the wheel loose which knocks everything else out of alignment.

Steel cables will stretch over time, especially if you store them under tension like leaving your bike in a low gear overnight. It's worthwhile learning how to adjust them as they need it done periodically.

You'll need some basic tools, depending on your bike, generally:

a shifter (adjustable/shifting spanner) or a socket set

phillips head screwdriver

allen keys

After you do any work, do a short test ride out of traffic and harms way in case something goes wrong e.g. your brakes don't work as expected or your wheel locks up.